Here's How 'Dunkirk' Maintains Its Intensity Through Sound Illusions

If you have not seen Christopher Nolan‘s latest film, the historical drama Dunkirk, it is perhaps one of the most intense films from start to finish. Of course aided by Nolan’s signature directorial moves and Hans Zimmer‘s musical magic, the film also makes use of an auditory illusion caused by Shepard tones to create its intense effect.

Named after cognitive scientist Roger Shepard, the Shepard tone consists of a superposition of sine waves separated by octaves. Explained by Vox, the middle octave remains at constant volume while the top one fades out and the bottom one fades in. This effect tricks the brain into thinking (and feeling) that the pitch is continually rising, thus creating an anxiety-inducing sound. Watch the breakdown above to see how crucial the Shepard tone is to Nolan’s Dunkirk.

Hans Zimmer’s work can also be found in several other Nolan films. In an interview with Business Insider, Nolan stated:

“There’s an audio illusion, if you will, in music called a ‘Shepard tone’ and with my composer David Julyan on The Prestige we explored that, and based a lot of the score around that. It’s an illusion where there’s a continuing ascension of tone. It’s a corkscrew effect. It’s always going up and up and up but it never goes outside of its range.

And I wrote the [Dunkirk] script according to that principle. I interwove the three timelines in such a way that there’s a continual feeling of intensity. Increasing intensity. I wanted to build the music on similar mathematical principals. So there’s a fusion of music and sound effects and picture that we’ve never been able to achieve before.”